It is well known in the logging machinery industry to mount a disc saw felling head at the end of a two boom support in which two hydraulic cylinders connected to the booms are manually operated simultaneously to guide the head horizontally towards and through a tree trunk as it is being cut.
Recent improvements to this conventional approach include the development of a dual boom support having two hydraulic cylinders connected by a compensating slave cylinder arranged by directed flow between the two main cylinders to maintain a constant vertical position of a mounted felling head as the support booms move the head. Another approach involves the use of a dual boom support having a pair of hydraulic cylinders under computer control to maintain the vertical position of the felling head as its position is adjusted by an operator.
Both of these approaches improve the cutting operation in that an operator is not required to balance the motion of two booms. These approaches still require the operation of two hydraulic cylinders during the cutting operation, albeit not directly by the operator, and the second approach additionally requires the inclusion and maintenance of microelectronics in a relatively hostile environment.
A different approach, known to the inventor, used in connection with a buncher, involves inclusion of a pair of pivotal links connecting a pair of booms. One of the links is connected to a hydraulic cylinder which is fixed in position while the head of the buncher is being moved horizontally. This mechanical arrangement is described in more detail below, but it has the advantage that only one of a pair of hydraulic cylinders is generally required to be operated to move the head horizontally. The operation is thus relatively simple for the operator, and the operation of a single cylinder is more energy efficient. One problem with this known arrangement, as it might by applied to tree felling, is its arrangement of links and the fixed hydraulic cylinder connected above one of the booms. Such an arrangement in a tree feller has the disadvantage of exposing the links and locking cylinder to damage from falling tree trunks, branches, etc.